The present invention relates to a hydraulic control device of an automatic transmission mounted on a vehicle, especially relating to a control at a time of failure in power distribution to a solenoid valve for hydraulic control, and belongs to a technical field of automatic transmissions for vehicles.
An automatic transmission mounted on a vehicle automatically switches gear position by selectively coupling a plurality of friction elements according to an operating state of the vehicle, and is equipped with a hydraulic control device for controlling the coupling of the friction elements. The hydraulic control device is provided with, for example, a switch valve for switching oil paths therebetween leading to the respective friction elements, and a hydraulic control valve for controlling a coupling hydraulic pressure to be supplied to each friction element. At least one of these valves is configured by a solenoid valve, and the solenoid valve is actuated by an electric signal from a controller and performs, for example, the switch between the oil paths and the control of the hydraulic pressure.
However, in using the solenoid valve in the hydraulic control device as above, a failure in which power distribution to the solenoid valve is disrupted, such as, a connecting terminal disengagement or a power distribution line disconnection, (hereinafter, referred to as the “power distribution failure”) may occur, therefore, a countermeasure, that is, a fail safe measure is required to be provided. For example, JP2005-344741A discloses an invention relating to such a fail safe measure.
The fail safe measure in JP2005-344741A has a configuration including linear solenoid valves for friction elements, respectively. In this configuration, a sequence valve for switching its state between a normal communicating state and a failure communicating state is arranged between the linear solenoid valves and a manual valve, and an on/off solenoid valve for setting itself to an off state at the time of the power distribution failure, so as to switch the sequence valve to the failure communicating state, is provided. The manual valve and a drain port of the predetermined linear solenoid valve are configured to communicate in the failure communicating state. Further, a high/low switch valve for changing the state to a low-speed communicating state in a case where the gear position is changed to high in the failure communicating state, and the gear position is switched to an N-gear position range and then to a travel range again, is provided.
Thereby, the sequence valve transitions to the failure communicating state at the time of the power distribution failure, and the hydraulic pressure supplied from the manual valve is supplied to the high gear position or the low gear position via the high/low switch valve. Thereby, a predetermined gear position is set and travel of the vehicle can be continued.
However, in the invention disclosed in JP2005-344741A, as the fail safe measure, the sequence valve arranged between the manual valve and the linear solenoid valves for the friction elements and for switching its state between the normal communicating state and the failure communicating state, the on/off solenoid valve for switching the sequence valve to the failure communicating state at the time of the power distribution failure, and the high/low switch valve for switching the gear position between the high gear position and the low gear position are required, and thereby, the configuration of the hydraulic control device becomes complex and is increased in cost.
In order to solve the above problems, the present invention is configured as follows.